Water-insoluble organic matter resulting from the decomposition of food waste and calcium compounds produced by the decomposition of urine are deposited, for example, on the inner surfaces of drainpipes of kitchens and toilets. These deposits are generally termed scale and impedes the flow of drain. When the piping system has a small pipe diameter and many bent portions, the accumulation of scale will clog up the drainpipe.
The drainpipes for the kitchens and toilets in aircraft are under structural limitations of the fuselage and therefore have a piping structure comprising small pipes in a complex arrangement confined within a narrow space. The drainpipes are descaled frequently to avoid clogging. However, use of an inorganic acid, such as hydrochloric acid or sulfuric acid, which is strongly acidic and highly effective for removing scale not only causes degradation of the material of the drainpipe due to corrosion but also gives rise to environmental pollution due to the waste water resulting from washing. On the other hand, acetic acid or like weak acid, if used, fails to produce a satisfactory descaling effect and accordingly entails the necessity of periodically removing the drainpipe to physically descale the inside of the pipe. This work is uncomfortable and difficult and requires a long period of time, possibly causing trouble to the flight schedule.
We have already developed a descaling composition adapted to effectively dissolve scale for removal without using any strongly acidic inorganic acid (JP-A No. 2000-63890). This composition contains a hydroxycarboxylic acid and a sulfamic acid as effective components, is not only low in corrosive activity on the pipe material but also excellent in biodegradable properties and is therefore unlikely to cause environmental pollution. Initially this descaling composition was developed as a denture cleaning agent for removing plaque and tartar from dentures by dissolving. However, when the composition was used for removing scale from the drainpipes of galleys and toilets in aircraft since plaque and tartar consist generally of the same components as the scale on drainpipes, the composition was found to exhibit also an outstanding effect of descaling.
In addition to corrosion resistance, lightweightness is also required of the galleys and toilets in aircraft as important properties, so that titanium or a titanium alloy containing titanium and other metal elements (hereinafter referred to merely as “titanium material”) Is favorably used for making these pipes. The titanium material has very high corrosion resistance because a titanium oxide coating, which exhibits high adhesion to the surface of the titanium material, is instantaneously formed on the titanium material when the material is exposed to the atmosphere to protect the base material with the coating. The titanium oxide coating is nevertheless easily removable If brought into contact with a chemical agent containing a strong acid since the coating has a very small thickness. When a strongly acidic descaling agent is used for removing scale, the scale is removed first, and the underlying oxide film is subsequently removed. If the application of the descaling agent is continued in this state, the surface of the titanium material is corrosively acted on by the descaling agent to release titanium ions into the agent on dissolving. If the application of the descaling agent is discontinued on completion of removal of the scale, titanium ions can be inhibited from dissolving out, whereas difficulty is actually encountered in controlling the work at such good timing. For this reason, it is actually impossible to obviate dissolving out of titanium ions in removing scale from drainpipes of titanium material.
An object of the present invention is to provide a composition for removing scale deposited on drainpipes of titanium material which composition has excellent activity to dissolve the scale while effectively inhibiting titanium ions from dissolving out (having a reduced likelihood of permitting titanium ions to dissolve out).